1. Field of the Invention
The present invention relates to a method of flow management in a packet-switched telecommunications network, more particularly in a network implementing the Internet Protocol (IP).
Although this is not limiting on the invention, the invention applies especially to methods used to meet the requirements of a flow-level admission control mechanism.
2. Background of the Invention
In the context of the present invention, a flow is identified by a set of attributes present in the header of the packets that constitute it (examples of attributes are source and destination IP addresses, source and destination ports, protocol, flow label, etc.).
All packets having the same values of these attributes constitute a flow.
At any given time, a flow is considered to be active if the time that has elapsed since observation of its last packet is less than a predetermined time-out period (which is typically of the order of a few seconds).
Proposed below is a solution for determining with a certain probability whether a packet received, for example over a link, belongs to an active flow or to a new flow.
The invention proposes a solution for determining with a certain probability whether a packet received, for example over a link, belongs to an active flow or to a new flow.
The proposed solution has the following particular feature: any flow identified as new is certain to be new.
Nevertheless, it is accepted that certain new flows are not detected.
The problem of detecting new flows arises in the context of a “flow aware” network architecture.
In such an architecture, new flows are identified “on the fly”, i.e. when packets are detected, and are subject to implicit admission control, without using signaling.
This form of admission control rejects packets that belong to new flows if a link or a path is congested, for example.
Proposed below is a much less complex solution to the problem of detecting new flows in the context of implicit admission control. It can advantageously be used for other applications, for example for counting flows.
A mechanism for identifying new flows that is based on detecting the SYN or SYNACK packet that signals the setting up of a TCP connection is known in the art, in particular from the document “Non-intrusive TCP Connection Admission Control for Bandwidth Management of an Internet Access Link”, IEEE Communication Magazine, May 2000 (Kumar, Hegde et al.). That method therefore applies only to applications using the TCP transport protocol.
A mechanism for identifying new flows based on keeping a list of all the current flows is known from the document “Quality of service and flow-aware admission control in the Internet”, Computer Networks, Vol. 40, pages 57-71 (Benameur et al.).
That mechanism has the drawback that it is necessary to delete flows from the list at the end of an inactivity time greater than the flow time-out period, failing which there would be a risk of saturation and, in any event, an increase in the time to look up a flow in the list.
Solutions enabling new flows to be identified in real time are known from the document “Designs for High-Speed Routers: Architecture and Performance Evaluation”, IEEE Transactions on Computers, Vol. 51, No. 9, September 2002, (Singhal et al.). One of those solutions also uses a data structure of variable size that cannot be addressed directly (a table combined with a chained list), and the time taken to look up a flow in the storage structure therefore increases with the number of flows. The other proposed solution requires the use of additional overflow memories if it is no longer possible, for want of space, to insert a new flow into the main data structure.